1. Field of the Invention
This invention relates to extrusion nozzles and a complete injection molding system nozzle assembly. The nozzle is particularly applicable in the production of articles comprisig structural or dense foam.
2. Description of the Prior Art
In the production of molded articles of dense foam, a problem exists in that the system produces an imperfection, known as a splash or splay mark, near the point of plastic injection. Since multiple gates or injection ports, are often required, several splay mark areas are frequent on structural foam pieces.
This nozzle is applicable for use in any injection molding system but we believe that it will find its greatest use in the production of dense foam parts. These can be comparatively large pieces weighing several pounds.
The particular method and apparatus used in producing these parts is well known in the art and reference to Angell, Jr., U.S. Pat. No. 3,268,636 (1966) and DeVita, U.S. Pat. No. 3,746,492 (1973) is made for a general description of the operation. These patents are incorporated herein by reference. In summary, a thermoplastic material is extruded, a foaming agent such as nitrogen is added, and a sufficient amount of the mixture to fill a subsequent mold is accumulated in an accumulator. When the mold is closed, a quick acting nozzle is opened and the thermoplastic material in the accumulator is rapidly injected into the mold after which the nozzle valve is closed. A difficulty which has been encountered in the production of these dense foam articles is an imperfection near the gate area, this imperfection usually appearing different in color and surface finish than the surrounding surfaces. Since multiple gates are required in larger articles, several splay mark areas are frequent on structural foam pieces. These lead to customer rejection of otherwise acceptable parts.